Method for bleaching with peroxyacids



United States Patent 3,521,992 METHOD FOR BLEACHING WITH PEROXYACIDS Bernard K. Easton, Pennington, N.J., assignor to FMC Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 13, 1967, Ser. No. 682,557 Int. Cl. D061 3/02 U.S. Cl. 8-111 Claims ABSTRACT OF THE DISCLOSURE Polyester fibers can be bleached with peracetic acid without developing dark stains by carrying out said bleaching in the presence of at least about 0.025% by weight of either hexamethylenetetramine or trioxane.

BACKGROUND OF THE INVENTION Field of the invention The invention covers bleaching of polyester textile fibers and goods therefrom using a bleach solution containing peracetic acid (also termed peroxyacetic acid).

Description of the prior art It is known that aqueous solutions of peroxygen compounds are suitable for bleaching textile fibers in the form of loose, fiber material as well as spun, woven or knitted goods consisting of native or artificial fibers of cellulose, or of synthetic fibers. Among the peroxy compounds which have been found effective as bleaching agents, monoperacetic acid has been extensively used because it has excellent bleaching activity without damaging the fibers of the bleached goods. This is due, in part, to the fact that monoperacetic acid can bleach goods under acid conditions. Other active oxygen bleaches require alkaline solutions which are more prone to attack fibers than are the acidic bleach solutions of peracetic acid.

One problem that has arisen in using peracetic acid to bleach polyester fibers, or spun, woven or knitted goods containing polyester fibers, is that dark brown stains often develop on the bleached goods. These stains are of varying diameters and are sporadically located over the surface of the goods without any apparent pattern. Moreover, it has been noticed that these stains do not occur in cloths produced from natural cellulosic fibers, e.g., cotton, but instead appear in one type of synthetic fiber, namely the polyester fiber-containing goods, e.g., Dacron or Dacron and cotton blends.

OBJECTS OF THE INVENTION It is an object of the present invention to bleach polyester fiber-containing goods with aqueous, peracetic acidcontaining bleach solutions without the formation of dark stains on the bleached goods.

This and other objects will be apparent from the fol lowing description of the invention.

SUMMARY OF THE INVENTION It has now been found that polyester fibers and materials containing these fibers can be bleached without developing stains by Wetting the polyester fibers with an aqueous solution containing 0.25 to 1.25% by weight of peracetic acid and atvleast 0.025% (and preferably 0.05 to 0.5%) of hexamethylenetetramine or trioxane, and heating the impregnated fibers or material at temperatures from about 150 to 212 F. for at least one-half hour.

It has been found further that best bleaching is obtained when the above bleaching process is carried out in the presence of from 0.1 to 0.5% of a water-soluble, alkali metal polyphosphate, preferably, sodium tripolyphosphate.

3,521,992 Patented July 28, 1970 In carrying out the present invention, an aqueous peracetic acid bleach solution is first made up. The peracetic acid can be supplied either as preformed peracetic acid or may be made just prior to use by any conventional in-situ method. In producing preformed peracetic acid, hydrogen peroxide and glacial acetic acid are reacted together in the presence of sulfuric acid, as a catalyst, to form peracetic acid. This is most conveniently sold as 40% peracetic acid and is available to the industry in that concentration. In the in-situ process, peracetic acid is formed by reacting hydrogen peroxide and acetic anhydride to yield a mixture of peracetic acid, residual hydrogen peroxide and acetic acid. One in-situ process which is effective is that described in U.S. Pat. 3,227,655, issued to Konrad Prett et al. on Jan. 4, 1966.

In the makeup of the bleach solution the peracetic acid, whether in-situ or preformed, is diluted with water so that the solution contains 0.25 to 1.25% of peracetic acid. The pH of the bleach solution should be on the order of about 5.5 to about 7.0, and preferably about 5 .5 to about 6.0. The pH of the bleach solution is adjusted by adding ammonium hydroxide and acetic acid, as required, to reach the desired pH level.

It is also desirable to add phosphates, particularly the water-soluble polyphosphates, such as sodium tripolyphosphate, tetrasodium pyrophosphate, sodium hexametaphosphate and long-chained polyphosphates normally termed, polyphosphate glasses. These glasses are produced by condensing molecules of sodium orthophosphate to form long chains of molecules having POP bonds, and should have a chain length sufficiently small to allow sufficient solubility in the solution, Typical polyphosphates include Sodaphos, having a chain length of about 6 and a P 0 content of 63.8% by Weight, Hexaphos, having a chain length of about 13 and a P 0 content of 67.5% by Weight and other such glasses having chain lengths up to about 20. The phosphates are added in amounts sufficient to supply about 0.1 to 0.5% of the bleach solution. To the above solution is then added at least 0.025% (and preferably 0.05 to 0.5%) of hexamethylenetetramine or trioxane. Larger amounts of either hexamethylenetetramine or trioxane can be employed but do not improve the stain-inhibiting eifect.

The polyester-containing fibers or goods which are to be bleached are placed in a saturator containing the above solution and removed with a 50 to 150% by weight pickup of the bleach solution. The exact bleach solution pickup is not critical, but about has been found eifective in obtaining the desired bleach without removing excessive bleach solution from the saturation. The temperature of bleach solution being applied is not critical, so long as it is below that at which peracetic acid becomes unstable, and ambient temperatures are most conveniently used.

After saturating the polyester fibers or goods, they are heated by contact with steam or steam-air mixtures at temperatures of from to 212 F. The time of treatment will vary depending upon the degree of bleach desired and the original condition of the fibers and/or cloth. The time of bleaching may vary from thirty minutes up to four hours; however, most bleaching is conducted within a period of about forty minutes to about two hours. After steaming of the bleach-impregnated goods, the goods may be washed, dried and packaged. In some cases, washing of the cloth is not necessary, and it is directly fed to subsequent stages, e.g., dyeing, etc. for further processing.

The fibers which are most responsive to bleaching by the above bleach solution without staining are the polyester fibers, particularly those such as Dacron and Avlin. These polyesters are of the terephthalic acid type.

The operation of the present process to yield a bleached cloth which is free of dark stains is not completely understood. Without in any way intending to limit or restrict the scope of the invention, the following theory is offered by way of explanation.

with steam at the temperatures and for the period of time set forth in Table 1. In order to reduce the temperature in the steam tube below 212 F., air was mixed with steam before it was passed into the steam tube in contact with the saturated woven fabrics. The bleached samples were then removed and observed for stains prior to being rinsed and dried.

TABLE 1 Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Control Control Control Control Control Control Hydrogen Peroxide (100% basis) 0. 040 0. 040 0.051 0.051 0. 051 0.051 0. 019 0. 010 0.051 0.051 0.051 0.051 Pei-acetic Acid (100% basis) 0. 52 0. 52 0. 53 0. 52 0. 52 0. 52 0. 52

IIMT 1 Hydrogen Peroxide (100% basis) Peracetic Acid (100% basis) lIMT l STPP Temperature F.) Time thrs.) Staining Run 13 Run 14 Run 15 Run 16 Run 17 Control Control Control Control C ontrol Hydrogen Peroxide (100% basis). 0.10 0. 10 0. 10 0. 10 0. 049 0. 049 0. 040 0. 049 0. 049 0. 040 gqrlaiz etic Acid (100% basis) 0. 53 0. 53 0. 53 0. 5 0. 52 0. 52 O. 52 0. 52 0. 52 0. 52

Trioxane Temperature C F.) Time (hrs.) Staining 1 Hexamethylenetetramino. 2 Sodium tripolyphosphate. No'rE.St=Strains; No St=N0 Stains.

It is known that some of the metal catalysts which are used in the production of the polyester fiber remain in the fiber after manufacture. These metal catalysts, particularly manganese ions, are believed to discolor the cloth during the bleaching process. Further, the degree of discoloration apparently depends in part on the intensity of the bleaching process. That is, when bleaching takes place at higher temperatures, i.e., 190 to 212 F. for extended periods up to three hours, there appears to be a greater tendency for these metallic cations to stain the cloth during the bleaching process. It is believed that in some way the hexamethylenetetramine, or trioxane additive, prevents these metallic ions from reacting with the bleach solution and being converted into forms which stain the polyester fiber or goods formed from the fibers. It is further noted that in the case of hexamethyllenetetramine, this additive must be introduced into the bleach solution in a preformed state in order to be operative. That is, the addition of ammonia and formaldehyde (which are the precursors of hexamethylenetetramine) to the bleach solution does not have this etfect of preventing staining as does hexamethylenetetramine. This is somewhat surprising, since ammonia and formaldehyde will react under normal, ambient conditions to form hexamethylenetetramine.

The following examples are given to illustrate the invention but are not deemed to be limiting thereof.

EXAMPLE 1 A number of bleaching runs were carried out as follows. Bleach solutions were made up by mixing peracetic acid and water to give the concentrations set forth in Table 1. The bleach solutions also had varying amounts of sodium tripolyphosphate, hexamethylenetetramine and/ or trioxane as set forth in Table 1. The residual hydrogen peroxide content of these bleach solutions is set forth in Table 1. Woven fabrics constructed of blended yarns containing 65% Dacron and cotton were saturated in the various bleach solutions until they picked up 100% of their weight of the bleach solution. The saturated fabrics then were placed in a steam tube and contacted Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure otherwise than as specifically described and exemplified herein.

What is claimed is:

1. Process for bleaching terephthalate polyester fibers and goods containing these fibers comprising wetting said fibers with an aqueous solution consisting essentially of 0.25 to 1.25% of peracetic acid and at least 0.025% of a member selected from the group consisting of trioxane and hexamethylenetetramine, heating the impregnated fibers at a temperature of from about to 212 F., and recovering bleached fibers which are free of stains.

2. Process of claim 1 wherein said member selected from the group consisting of hexamethylenetetramine and trioxane is present in amounts of about 0.05 to 0.5%.

3. Process of claim 1 wherein said aqueous solution containing peracetic acid also contains from 0.1 to 0.5% of a water-soluble alkali metal polyphosphate.

4. Process of claim 3 wherein said alkali metal polyphosphate is sodium tripolyphosphate.

5. Process of claim 1 wherein said aqueous solution contains at least 0.025% of hexamethylenetetramine.

References Cited UNITED STATES PATENTS MAYER WEINBLATT, Primary Examiner US. Cl. X.R. 8-101 

